The present invention relates to a toothed belt of elastomeric material for a belt drive consisting of a toothed belt and a gear wheel, with crown surfaces of the teeth of the belt being seated on the bases of the grooves of the gear wheel. The present invention also relates to a method of making such a toothed belt.
With the construction principle for producing toothed belt drives as known, for example, from DE-AS 27 21 800, the height of the belt teeth is less than the depth of the grooves of the gear wheel, with the bases of the grooves of the belt provided between the belt teeth resting upon the heads of the teeth of the gear wheel. A more advantageous construction principle is known, for example, from DE-AS 11 97 710, where the height of the belt teeth is greater than the depth of the gear wheel grooves, with the crown surfaces of the teeth of the belt being seated upon the bases of the gear wheel grooves. Pursuant to this construction principle, the entire radial height of the sides of the gear wheel are utilized for a power-transferring tooth side contact with the teeth of the belt, which manifests itself in an advantageous manner with regard to the surface pressure against the sides of the belt teeth, especially with the frequently very small radial side heights that exist. Although this is not important for the strength of the generally metal gear wheel when in order to increase the proportion of the force transfer due to friction between the contact surfaces of the toothed belt and gear wheel, which abut one another in the radial direction, within a predetermined tooth pitch, the peripheral spacing of the gear wheel teeth is great and in conformity therewith the peripheral length of the gear wheel teeth is small, none the less where the toothed belt is made of plastic or a similar material, the length of the bases of the belt teeth and hence the shearing strength of the belt teeth, is increased.
With a toothed belt drive of the aforementioned general type, where the height of the belt teeth is greater than the depth of the grooves of the gear wheel, and the crown surfaces of the belt teeth are seated upon the bases of the gear wheel grooves, as the length of the crown surfaces of the belt teeth in the circumferential direction of the belt increases in order to increase the force-transferring portion via friction, the noise also increases, which results as the belt teeth run up into the gear wheel grooves and is caused when the crown surfaces of the belt teeth strike the bases of the gear wheel grooves. Normally, with conventional tooth profiles the belt tooth, without meshing with the gear wheel, is somewhat shorter than the gear wheel groove in the direction of rotation of the belt drive in order for the belt teeth to be able to satisfactorily run up into the gear wheel grooves. However, for reversible toothed belt drives, it is often important and indispensible that when the belt tooth meshes with the gear wheel, the belt tooth contact both sides of the gear wheel groove without play. With the elastomeric material that is utilized in producing toothed belts, and that fulfills the requirements for strength and stability of the toothed belt and the belt teeth, which material is, for example, generally the plastic polyurethane, it is nearly impossible with the conventional operative belt tensions to such a way that the material can completely fill the gear wheel groove in a manner free of play as a result of a spreading that displaces the radial compression of the material volume of the belt tooth. A precondition for this would be a nearly already free-of-play meshing of the belt tooth in the gear wheel groove, and in order to then additionally obtain a satisfactory running-up of the belt teeth into the gear wheel grooves, complicated tooth shapes or tooth profiles would be necessary that would, of course, considerably increase the cost not only for manufacturing the toothed belt, but also for manufacturing the gear wheels that cooperate with the toothed belts during operation of a toothed belt drive.
It is therefore an object of the present invention to provide a toothed belt of the aforementioned general type where the noise that is generated when the toothed belt runs up onto a gear wheel is dampened and reduced, and where the belt teeth, prior to engagement with the gear wheel, are somewhat shorter in the direction of rotation than are the gear wheel grooves in order to be able to satisfactorily run up into the gear wheel grooves, yet where it is possible for the belt teeth to contact both sides of the gear wheel grooves in the free-of-play manner that is required for a reversible toothed belt drive.